11 research outputs found
IST Austria Thesis
This work is concerned with two fascinating circuit quantum electrodynamics components, the Josephson junction and the geometric superinductor, and the interesting experiments that can be done by combining the two. The Josephson junction has revolutionized the field of superconducting circuits as a non-linear dissipation-less circuit element and is used in almost all superconducting qubit implementations since the 90s. On the other hand, the superinductor is a relatively new circuit element introduced as a key component of the fluxonium qubit in 2009. This is an inductor with characteristic impedance larger than the resistance quantum and self-resonance frequency in the GHz regime. The combination of these two elements can occur in two fundamental ways: in parallel and in series. When connected in parallel the two create the fluxonium qubit, a loop with large inductance and a rich energy spectrum reliant on quantum tunneling. On the other hand placing the two elements in series aids with the measurement of the IV curve of a single Josephson junction in a high impedance environment. In this limit theory predicts that the junction will behave as its dual element: the phase-slip junction. While the Josephson junction acts as a non-linear inductor the phase-slip junction has the behavior of a non-linear capacitance and can be used to measure new Josephson junction phenomena, namely Coulomb blockade of Cooper pairs and phase-locked Bloch oscillations. The latter experiment allows for a direct link between frequency and current which is an elusive connection in quantum metrology. This work introduces the geometric superinductor, a superconducting circuit element where the high inductance is due to the geometry rather than the material properties of the superconductor, realized from a highly miniaturized superconducting planar coil. These structures will be described and characterized as resonators and qubit inductors and progress towards the measurement of phase-locked Bloch oscillations will be presented
Tuning random lasing in photonic glasses
We present a detailed numerical investigation of the tunability of a
diffusive random laser when Mie resonances are excited. We solve a multimode
diffusion model and calculate multiple light scattering in presence of optical
gain which includes dispersion in both scattering and gain, without any
assumptions about the parameter. This allows us to investigate a
realistic photonic glass made of latex spheres and rhodamine and to quantify
both the lasing wavelength tunability range and the lasing threshold. Beyond
what is expected by diffusive monochromatic models, the highest threshold is
found when the competition between the lasing modes is strongest and not when
the lasing wavelength is furthest from the maximum of the gain curve
Disordered Cellulose-based Nanostructures for Enhanced Light-scattering
Cellulose is the most abundant bio-polymer on earth. Cellulose fibres, such
as the one extracted form cotton or woodpulp, have been used by humankind for
hundreds of years to make textiles and paper. Here we show how, by engineering
light matter-interaction, we can optimise light scattering using exclusively
cellulose nanocrystals. The produced material is sustainable, biocompatible
and, when compared to ordinary microfibre-based paper, it shows enhanced
scattering strength (x4) yielding a transport mean free path as low as 3.5 um
in the visible light range. The experimental results are in a good agreement
with the theoretical predictions obtained with a diffusive model for light
propagation
Quantum electromechanics of a hypersonic crystal
Radiation pressure within engineered structures has recently been used to
couple the motion of nanomechanical objects with high sensitivity to optical
and microwave electromagnetic fields. Here, we demonstrate a form of
electromechanical crystal for coupling microwave photons and hypersonic phonons
by embedding the vacuum-gap capacitor of a superconducting resonator within a
phononic crystal acoustic cavity. Utilizing a two-photon resonance condition
for efficient microwave pumping and a phononic bandgap shield to eliminate
acoustic radiation, we demonstrate large cooperative coupling ()
between a pair of electrical resonances at GHz and an acoustic resonance at
GHz. Electrical read-out of the phonon occupancy shows that the
hypersonic acoustic mode has an intrinsic energy decay time of ms and
thermalizes close to its quantum ground-state of motion (occupancy ) at a
fridge temperature of mK. Such an electromechanical transducer is
envisioned as part of a hybrid quantum circuit architecture, capable of
interfacing to both superconducting qubits and optical photons.Comment: 16 pages, 12 figures, 8 appendice
Geometric superinductance qubits: Controlling phase delocalization across a single Josephson junction
There are two elementary superconducting qubit types that derive directly
from the quantum harmonic oscillator. In one the inductor is replaced by a
nonlinear Josephson junction to realize the widely used charge qubits with a
compact phase variable and a discrete charge wavefunction. In the other the
junction is added in parallel, which gives rise to an extended phase variable,
continuous wavefunctions and a rich energy level structure due to the loop
topology. While the corresponding rf-SQUID Hamiltonian was introduced as a
quadratic, quasi-1D potential approximation to describe the fluxonium qubit
implemented with long Josephson junction arrays, in this work we implement it
directly using a linear superinductor formed by a single uninterrupted aluminum
wire. We present a large variety of qubits all stemming from the same circuit
but with drastically different characteristic energy scales. This includes flux
and fluxonium qubits but also the recently introduced quasi-charge qubit with
strongly enhanced zero point phase fluctuations and a heavily suppressed flux
dispersion. The use of a geometric inductor results in high precision of the
inductive and capacitive energy as guaranteed by top-down lithography - a key
ingredient for intrinsically protected superconducting qubits. The geometric
fluxonium also exhibits a large magnetic dipole, which renders it an
interesting new candidate for quantum sensing applications.Comment: 11 pages, 7 figure
A superconducting qubit with noise-insensitive plasmon levels and decay-protected fluxon states
The inductively shunted transmon (IST) is a superconducting qubit with
exponentially suppressed fluxon transitions and a plasmon spectrum
approximating that of the transmon. It shares many characteristics with the
transmon but offers charge offset insensitivity for all levels and precise flux
tunability with quadratic flux noise suppression. In this work we propose and
realize IST qubits deep in the transmon limit where the large geometric
inductance acts as a mere perturbation. With a flux dispersion of only 5.1 MHz
we reach the 'sweet-spot everywhere' regime of a SQUID device with a stable
coherence time over a full flux quantum. Close to the flux degeneracy point the
device reveals tunneling physics between the two quasi-degenerate ground states
with typical observed lifetimes on the order of minutes. In the future, this
qubit regime could be used to avoid leakage to unconfined transmon states in
high-power read-out or driven-dissipative bosonic qubit realizations. Moreover,
the combination of well controllable plasmon transitions together with stable
fluxon states in a single device might offer a way forward towards improved
qubit encoding schemes.Comment: 13 pages, 8 figure
Compact vacuum-gap transmon qubits: Selective and sensitive probes for superconductor surface losses
State-of-the-art transmon qubits rely on large capacitors, which systematically improve their coherence due to reduced surface-loss participation. However, this approach increases both the footprint and the parasitic cross-coupling and is ultimately limited by radiation losses—a potential roadblock for scaling up quantum processors to millions of qubits. In this work we present transmon qubits with sizes as low as 36 × 39 µm2 with 100-nm-wide vacuum-gap capacitors that are micromachined from commercial silicon-on-insulator wafers and shadow evaporated with aluminum. We achieve a vacuum participation ratio up to 99.6% in an in-plane design that is compatible with standard coplanar circuits. Qubit relaxationtime measurements for small gaps with high zero-point electric field variance of up to 22 V/m reveal a double exponential decay indicating comparably strong qubit interaction with long-lived two-level systems. The exceptionally high selectivity of up to 20 dB to the superconductor-vacuum interface allows us to precisely back out the sub-single-photon dielectric loss tangent of aluminum oxide previously exposed to ambient conditions. In terms of future scaling potential, we achieve a ratio of qubit quality factor to a footprint area equal to 20 µm−2, which is comparable with the highest T1 devices relying on larger geometries, a value that could improve substantially for lower surface-loss superconductors
Compact vacuum gap transmon qubits: Selective and sensitive probes for superconductor surface losses
This dataset comprises all data shown in the figures of the submitted article "Compact vacuum gap transmon qubits: Selective and sensitive probes for superconductor surface losses" at arxiv.org/abs/2206.14104. Additional raw data are available from the corresponding author on reasonable request
Friction forces determine cytoplasmic reorganization and shape changes of ascidian oocytes upon fertilization
Contraction and flow of the actin cell cortex have emerged as a common principle by which cells reorganize their cytoplasm and take shape. However, how these cortical flows interact with adjacent cytoplasmic components, changing their form and localization, and how this affects cytoplasmic organization and cell shape remains unclear. Here we show that in ascidian oocytes, the cooperative activities of cortical actomyosin flows and deformation of the adjacent mitochondria-rich myoplasm drive oocyte cytoplasmic reorganization and shape changes following fertilization. We show that vegetal-directed cortical actomyosin flows, established upon oocyte fertilization, lead to both the accumulation of cortical actin at the vegetal pole of the zygote and compression and local buckling of the adjacent elastic solid-like myoplasm layer due to friction forces generated at their interface. Once cortical flows have ceased, the multiple myoplasm buckles resolve into one larger buckle, which again drives the formation of the contraction pole—a protuberance of the zygote’s vegetal pole where maternal mRNAs accumulate. Thus, our findings reveal a mechanism where cortical actomyosin network flows determine cytoplasmic reorganization and cell shape by deforming adjacent cytoplasmic components through friction forces